My 1991 Honda Civic now has four new Goodyear tires. The technicians filled them
to 30 psi and recorded this. I pointed out that Honda recommended 26 psi for my
car. The shop said they'd be happy to lower it to this but implied that 30 psi
was customary. I figured they had their reasons and decided to research and
adjust according to what I found.

I did a groups.google search. It seems people are about evenly divided on using
the manufacturer's pressure and using a pressure say 4 psi or so higher. The
lower pressure gives a more comfortable ride. The higher pressure supposedly
gives better handling and longer tire life.

Has anyone run their own experiment, trying the manufacturer's pressure for the
life of one set of tires, then at some time trying a pressure a few psi higher
for another set of tires?

I hadn't started watching my tire pressure that closely (about once a month now)
until just a few years ago, so I don't have a good "database."